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Increased frequency of viral loads above 100000 HIV-1 RNA copies/ml measured by Roche Cobas TaqMan assay in comparison with Cobas Amplicor assay

Background: The International AIDS Society-USA Antiretroviral Guidelines Panel recently raised concerns over results of several evaluation studies that consistently reported increased frequency of detectable plasma viremia by the Cobas TaqMan assay for HIV-1 RNA quantification version 1. (Roche, USA, real-time PCR) in a substantial proportion of treated patients who were previously considered complete virological responders based on undetectable plasma viremia measured by the standard Cobas Amplicor assay (conventional PCR). A second version of the TaqMan assay (version 2) became commercially available in 2009. Aim: The aim of this study was to compare HIV-1 viral loads obtained by TaqMan assay v2.0 and standard Cobas. Amplicor assay in clinical samples. Materials and methods: The study enrolled 44 newly-diagnosed HIV-1 infected persons (39 patients: genotype B, 3 patients: genotype A, 2 patients: genotype C), with detectable viral load (>50 copies/ml of plasma) that entered clinical care at the national Reference center for HIV/AIDS in the period 2006-2008. SAS v9.1 software was used for statistical analysis, and the degree of agreement between the two techniques was represented by Bland and Altman plot. Results: Median values (range) were 4.68 (3.27-5.91) and 4.91 (3.67-6.90) log10 HIV-1 RNA copies/ml for the Amplicor and TaqMan assays, respectively. The plot of identity of TaqMan v2.0 and Amplicor assays viral load measurements indicated that TaqMan v2.0 assay measurements are generally higher than Amplicor assay measurements. The Bland-Altman plot indicated that the 95% limits of agreement between the two methods were asymmetrical and ranged from -1.39 to 0.69. The number of patients with a viral load >5 log10 HIV-1 RNA copies/ml was higher when using the TaqMan v2.0 assay (45%, 20 of 44 patients) compared with Amplicor assay (30%, 13 of 44 patients). Conclusion: In conclusion, TaqMan assay v2.0 provides consistently higher values of plasma viremia in newly-diagnosed patients (majority with genotype B) at entrance to care compared with standard Amplicor assay. Clinical implications and long-term prognostic significance of higher plasma viremia (particularly above 5.0 log10 HIV-1 RNA copies/ml) reported by TaqMan assay v2.0 in patients entering care should be carefully evaluated in the future.

HIV-1 ; Roche Cobas TaqMan ; Cobac Amplicor assay

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